What causes steel wool to rust?

Rust results from a chemical interaction between iron and oxygen, commonly referred to as iron oxide. Since steel wool, like most steel, is mainly composed of iron, it is vulnerable to rust unless coated with a rust-resistant layer. This reaction happens when two iron atoms combine with three oxygen atoms in water. The oxygen bonds with the metal, creating a new compound.

While the air is rich in oxygen, steel wool won't rust just by being left out. The key to rust formation is water, or hydrogen hydroxide (H2O). When steel wool becomes wet, water infiltrates the tiny crevices in the metal. The water acts as an electrolyte, drawing electrons from the oxygen toward the iron. The hydrogen bond in water serves as an acid, contributing to rust's corrosive nature. Saltwater accelerates the corrosion process, making it even more harmful to rust-prone metals. As steel wool corrodes, it releases heat.

To prevent steel wool from rusting, you can interrupt the rusting process by eliminating one of the necessary components: iron, oxygen, or water. This can be achieved by coating the steel wool with a protective layer that blocks oxygen and water. If steel wool does rust, it's often easier to replace it rather than spend time removing the rust, as this process can be tedious. Generally, rust is undesirable because it deteriorates the metal and compromises its strength. Rust isn't limited to steel and iron—aluminum can also rust, forming aluminum oxide.